A U.S. Border Patrol agent discovered a roadside bomb planted in the dirt along a known smuggling route west of Tucson in 2009, according to a secret memo leaked during last week’s hacking of Arizona Department of Public Safety email accounts.

The May 2009 memo, written by the Pima County Sheriff’s Department bomb squad and marked “not for public or media dissemination,” said the explosive detonated during the subsequent investigation. The document didn’t say whether anyone was hurt in the explosion.

The memo said the device appeared to be “moderately complex” in its construction. It was made out of pipe and wrapped in wires.

It was unclear to investigators at the time who planted the bomb or why. Law enforcement officers patrolling the area were told to be extra careful and to look out for similar devices. The investigation was handed off to the federal Bureau of Alcohol, Tobacco, Firearms and Explosives as well as the FBI.

Although investigators didn’t name any suspects in the memo, white supremacist groups in Arizona have talked in the past about putting explosives along the border to hurt or kill immigrants who illegally sneak into the U.S.

A year after the explosive was discovered, neo-Nazis were spotted at a Tea Party rally in Tempe, handing out fliers calling for landmines to be placed along the U.S.-Mexico border.

The new memo was among 700 files leaked by the hacker group LulzSec, which broke into the accounts of DPS employees last week. The group claimed the hack was in retaliation for Arizona passing harsh immigration laws last year.